There have been recently put into practical use, as display panels for display devices such as digital televisions, organic EL panels that include organic light-emitting elements arranged on a substrate in a matrix and rely on electroluminescence phenomenon of organic materials.
A commonly known structure of such organic EL display panels is that drive circuits (for example, including thin film transistor (TFT) elements) are disposed on a substrate, an insulating layer is disposed on the drive circuits, and organic light-emitting elements are further arranged on the insulating layer. The organic light-emitting elements each include, as the basic structure, an anode that is disposed on the insulating layer, a laminate that is disposed on the anode and is composed of a light-emitting layer made of an organic light-emitting material and a functional layer, and a transparent conductive cathode that is disposed on the laminate. Such organic light-emitting elements are current-driven light-emitting elements. When the organic light-emitting elements are driven, voltage is applied between each anode and the cathode, and holes and electrons injected to the light-emitting layer recombine with each other, and thus the organic light-emitting elements emit light.
According to the organic EL display panels, the organic light-emitting elements each form any one of respective subpixels of red (R), green (G), and blue (B) colors, and each adjacent red, green, and blue subpixels constitute a single pixel. It is important to improve the luminous efficiency and the life property of the respective organic EL elements of the R, G, and B colors, from the standpoint of reducing the power consumption, increasing the operating life of the organic EL display panels, and the like. The blue organic EL elements tend to have the shortest operating life among the respective organic EL elements of the R, G, and B colors, and accordingly there has been a problem that the operating life of the blue organic EL elements needs to be prolonged in order to prolong the operating life of display devices.
In view of the problem, Patent Literature 1 has proposed a technology of realizing luminous efficiency improvement, operating life prolonging, cost reduction in the manufacturing facilities, and productivity improvement in an organic EL display panel by using the nozzle printing method and the vacuum deposition method to adopt the multiphoton emission structure in which only blue light-emitting elements are stacked in two layers (see for example paragraph 0065). Specifically, red light-emitting layers, green light-emitting layers, and first blue light-emitting layers are formed by the wet deposition method, and then a charge generation layer is formed only in each blue subpixel region by the vacuum deposition method. Further, a second blue light-emitting layer is formed by the vacuum deposition method so as to cover the red light-emitting layers, the green light-emitting layers, and the charge generation layers. The second blue light-emitting layer exhibits an electron transport function on the red light-emitting layers and the green light-emitting layers, and functions as a blue light-emitting layer on the charge generation layers. Patent Literature 1 discloses that this structure realizes operating life prolonging of the blue organic light-emitting elements, cost reduction in the manufacturing facilities, and productivity improvement.